All posts tagged: Hubble constant

Our local universe’s expansion rate doesn’t add up, astronomers find

Our local universe’s expansion rate doesn’t add up, astronomers find

Published by Jenni Sidey

A difference of a few kilometers per second might not sound like much. In cosmology, it has become one of the field’s most stubborn problems. An international team of astronomers has now delivered one of the sharpest direct measurements yet of how fast the nearby Universe is expanding, and the answer again lands on the high side. Their new value for the Hubble constant, the number used to describe that expansion rate, is 73.50 ± 0.81 kilometers per second per megaparsec. That is just over 1% precision. It also keeps the long-running Hubble tension very much alive. The result, published in Astronomy & Astrophysics, comes from the H0 Distance Network Collaboration, or H0DN. The project grew out of a March 2025 workshop at the International Space Science Institute in Bern, Switzerland, where researchers from across the field worked to build a shared framework for combining local measurements of cosmic distance. This graphic represents the tension that exists between measurements of the expansion rate of the late, nearby Universe, versus what would be expected based on …

Expanding catalog of black hole collisions is rewriting the history of the universe

Expanding catalog of black hole collisions is rewriting the history of the universe

Published by Jenni Sidey

Between May 2023 and January 2024, a global network of gravitational-wave detectors picked up 128 new cosmic signals, more than doubling the entire catalog built across the previous decade. The universe, it turns out, is not quiet. It is constantly shaking. The LIGO-Virgo-KAGRA Collaboration, an international partnership spanning observatories in the United States, Italy, and Japan, has published its fourth gravitational-wave catalog, GWTC-4.0, in a forthcoming special issue of Astrophysical Journal Letters. The collection represents the most comprehensive census yet of colliding black holes and neutron stars, and it is already pushing physics into territory no one has mapped before. “The beautiful science that we are able to do with this catalog is enabled by significant improvements in the sensitivity of the gravitational-wave detectors as well as more powerful analysis techniques,” said Nergis Mavalvala, dean of the MIT School of Science and a member of the collaboration. The timeline of observing runs covering a time span starting from 2015 and lasting up to the beginning of O4b on 2024 April 10. The periods in which …

Ancient Milky Way stars challenge the age of the universe and the Hubble tension

Ancient Milky Way stars challenge the age of the universe and the Hubble tension

Published by Jenni Sidey

The oldest stars in the Milky Way are forcing a fresh look at one of cosmology’s biggest arguments. If some of them are about 13.6 billion years old, as a new analysis suggests, then the universe itself cannot be younger than that. That matters because astronomers still disagree on how fast the universe is expanding, a dispute known as the Hubble tension. One set of measurements, based on Cepheid stars and supernovae, points to a faster expansion rate and a younger universe, roughly 12.9 billion years old. Another, based on the cosmic microwave background, points to a slower expansion rate and an older universe, around 14.0 billion years old. The new study, published in Astronomy & Astrophysics, does not try to settle that argument by measuring expansion directly. Instead, researchers from the University of Bologna, the Leibniz Institute for Astrophysics Potsdam, and other institutes turned the problem into an age question: how old are the oldest stars close to home? Reading time in the Milky Way The logic is simple. The universe cannot be younger …

Scientists develop a new way to measure the expansion rate of the universe

Scientists develop a new way to measure the expansion rate of the universe

Published by Jenni Sidey

For years, cosmologists have argued over a simple question with an awkward answer: How fast is the universe expanding right now? The expansion rate, called the Hubble constant, ought to come out the same no matter how you measure it. Yet it does not. Measurements tied to the early universe, using relic signals like the cosmic microwave background, land in the high 60s when expressed in kilometers per second per megaparsec. Late-universe measurements, often anchored to exploding stars and the cosmic distance ladder, tend to land higher, in the low-to-mid 70s. The mismatch is now described as being in more than 5-sigma conflict, a level that keeps theorists awake at night. The problem has a name that has become almost too tidy for its stakes: the Hubble tension. This illustration and description from NASA, the European Space Agency, and the Space Telescope Science Institute lays out the three basic steps astronomers use to calculate the Hubble constant based on measurements in the modern universe. (CREDIT: NASA / ESA / Space Telescope Science Institute) The hum …

What a rare lensed supernova could mean for measuring cosmic expansion

What a rare lensed supernova could mean for measuring cosmic expansion

Published by Jenni Sidey

A burst of light in the deep sky is doing something it should not be able to do. It looks like one supernova, but it shows up as several copies at once, scattered around two foreground galaxies. The effect is not a telescope trick or a camera glitch. It is gravity, bending the path of the light so it reaches Earth along different routes, on different schedules. The object is SN 2025wny, nicknamed “SN Winny,” and it sits about 10 billion light-years away. It is also a superluminous supernova, a kind of stellar explosion so bright that it can still be detected from extreme distances. The team behind the work, from the Technical University of Munich (TUM), Ludwig Maximilian University (LMU), and the Max Planck Institutes for Astrophysics (MPA) and Extraterrestrial Physics (MPE), says the alignment is so unlikely that the odds of finding a similar event are below one in a million. That rarity is exactly why astronomers are excited. If they can measure the time gaps between the different images of the same …